Patent GB-931042-A (GB)
Title: A measuring device or the like for the indication of the amount of the displacement of a slide
IPC: G01D5/26
Filed: 1961-09-18
Abstract: 931,042. Electric selective signalling systems. M. HENSOLDT & SOHNE, OPTISCHE WERKE A.G. Sept. 18, 1961 [Sept. 23, 1960; Aug. 5, 1961], No. 33307/61. Class 40 (1). [Also in Groups XXII and XL (b)] In a system for measuring the relative displacement of a first body 2, Fig. 1, e.g. a machine tool slide, with respect to a scale 21 attached to a second body, e.g. a machine tool bed, the first body 2 is moved to its displaced position and then a scale-sensing contact 20 is moved, by a micrometer arrangement 14, 15 until the sensing contact registers exactly with a scale graduation-this being determined by an optical arrangement 3, 4, 5, 6, 7, 8, 9, 10, 11 which then images a mark M from the scale equally on two photo-electric cells 12, 13-and then the position of the body 2 with respect to the scale 21 is determined firstly by the position of the sensing contact 21 with respect to the scale, which provides the highest two significant digits, and secondly by the extent the sensing contact had to be moved with respect to the body 2 in order to achieve precise registration, which provides a further four lesser significant digits. The system described also has the feature that its " zero " can be arbitrarily displaced and a visual output by means of digit indicating glow discharge tubes is provided. Coarse measurement.-The scale 21, Figs. 1 and 4, consists of two rows of conductive strips dm, cm, and a continuous strip P to which a potential is connected. Individual connections as shown are taken from each of the dm and cm strips, to the cathodes of two glow discharge tubes (Fig. 6, not shown) and the scale is sensed by a single wide roller 20, Fig. 5a, which thus connects the potential on the continuous strip P to one each of the dm and cm strips. The " zero " of this scale can be displaced by sliding the scale from 1 to 10 cm. relative to the machine bed and by a switch (not shown) which alters the order in which the dm strips are connected to the indicating tube cathodes. Fine measurement.-The extent by which the sensing contact 20, Fig. 1, has to be displaced with respect to the body 2 is measured by determining the number of revolutions made by the micrometer screw 14. This is effected by a drum 30, Fig. 9, attached to the screw 14, the drum being rotatable but axially fixed, a fixed helix 31, a fixed cylinder 32, and two brushes 34, 36, the brush 34 being guided by a slot 33 in the helix and a slot 35 in the drum so that the brush follows the helix as the drum is rotated. The helix carries two series of contact strips and a common contact strip, exactly similar to the scale 21, and the cylinder carries a similar array of contacts except that in respect of the least significant digit only a " 0 " or a " 5 " indication is provided. Modifications.-If the machine tool bed is very long, thereby making the construction of a scale as in Fig. 1 difficult, a second drum, similar to that shown in Fig. 9 but driven by a rack on the machine bed can be used (Figs. 7 and 10, not shown). Displacement of the zero is made possible by incorporating a clutch in the mechanical drive. In this embodiment the zero of the fine scale can also be displaced by an arrangement which makes it possible to vary the mechanical coupling between the shaft 14 of Fig. 1 and the optical components.